I agree with most of your analyses, but I have issues with two cards. I have only played solitaire games with these cards thus far, so please feel free to let me know if I'm way off base.
Spice Merchant
$4 Action
You may trash a Treasure from your hand. If you do, choose one:
+2 Cards and +1 Action, or +$2 and +1 Buy
Moneylender is a solid opener, and this is like Moneylender, but slightly worse (though the +Buy can come in handy). You aren't guaranteed enough money, and its easier to accidentally trash everything and play yourself into a corner. Dies off eventually, and so benefits from trash-for-benefit cards.
It seems as if you're completely ignoring Spice Merchant's (+2 Cards/+1 Action), which I believe is the option you'll want to use the majority of the time you play Spice Merchant.
Moneylender lets you trash Copper while providing enough coins to allow you buy more powerful cards for your deck. Spice Merchant lets you trash Copper while allowing you to
draw and play more powerful cards that are already in your deck. So if there's a $3-cost card available that you want to play as often as possible (say Swindler or Ambassador), you might prefer to open with Spice Merchant rather than Moneylender.
That being said, I'm wondering if Spice Merchant isn't a better card to pick up soon
after your first reshuffle, rather than on one of your first two turns. Unlike Moneylender, Spice Merchant does not jump-start your economy, so buying it immediately may slow you down. If you buy better coin-producing cards on the first two turns, then buy a Spice Merchant on turn 3 or 4, you'll most likely be shuffling it into your deck along with a powerful $5 or $6 cost card. Then you can play Spice Merchant to trash Copper while cycling to your good stuff.
As for the (+2 Coins/+1 Buy) option, I'd probably only opt for it in specific, less common situations. First: I really need the +Buy. Second: the +2 coins are guaranteed to get me to a price point I really need, whereas the two cards I draw are not. Third: there are fewer than 2 cards in my deck and the +2 coins are enough to buy a card that my deck needs before I reshuffle.
Stables
$5 Action
You may discard a Treasure. If you do, +3 Cards and +1 Action.
Pretty awesome non-terminal drawer, probably equal to Hunting Party / Lab. Less reliable, though, and does very poorly when your Coppers are trashed. Does nicely with fuel from cards like Ill-Gotten Gains, Cache, and Trader.
Saying that it does nicely with fuel from those cards seems akin to buying more Copper to feed your Moneylender. Your deck starts with 7 Coppers. Stables are an alternative to aggressively trashing your Copper, much like Apothecary.